The efficient production of oil and gas from subsea wells requires the remote control of valves, which pass hydraulic fluid to actuate various well functions such as connectors, latches, valve actuators, flow control devices, and the like. Solenoid energized valve mechanisms are typically used for this purpose. The solenoids are energized by electrical energy transmitted through long power cables that extend from a surface based power source to the location of the valves. Because subsea solenoid valves for well control are inaccessible from the standpoint of service, high reliability is crucial. An example of a solenoid actuated valve for handling high pressure fluids is disclosed in U.S. Pat. No. 4,088,152 to Baugh. The Baugh device uses a solenoid to directly drive a valve gate having sliding shear seals, and incorporates roller bearings to reduce frictional loading.
Maintaining high levels of hydraulic fluid cleanliness through control lines is a challenge, partly because control lines can be many miles long. Valves constructed with sliding shear seals are well suited for reliable operation when high pressure fluids are contaminated with particulate. Larger valve seating forces generally correlate with higher reliability, and small seats with low seating force are less resistant to fluid borne contamination. A valve having shear seals is therefore often used for the main valve. A major disadvantage of shear type valve mechanisms is the large frictional force to which the valve mechanism is ordinarily subjected. Larger frictional forces cause larger power consumption of the valve actuator. Unfortunately, long control lines for carrying signals and electric power to valves limit the amount of current available to each valve. It is inefficient to directly drive a sliding type main valve with a solenoid.
A common approach that minimizes electrical power requirements is to use a small poppet-type solenoid valve to pilot the larger main valve. U.S. Pat. No. 4,848,404 to Hickok discloses an example of a piloted main valve, wherein the pilot valve is a low pressure poppet-type solenoid valve. Poppet type solenoid valves require very little electric power due to the small valve seat and the low force needed to move the valve element. A major disadvantage of poppet valves, however, is their decreased resistance to contamination. A typical solution to this problem is to provide a separate, low-pressure, and well-filtered fluid supply for the pilot valve. The reduced pressure keeps operating force low and reduces damage to the small seat while better filtration prevents failures caused by fluid contamination. This level of filtration is not typically required for slide valves. The shearing action of the hard metal seal edges of slide valves excludes fluid born contamination and accomplishes efficient sealing under circumstances that would interfere with the sealing capabilities of poppet valves.
Principally, the key to reducing the frictional forces of a sliding seal valve is to reduce the area of the sliding seal that is exposed to pressure. U.S. Pat. No. 4,856,557 discloses a valve having smaller sliding seals in order to reduce actuation force, but two seals are required to slide on their respective seal plates, which multiplies the actuation force. A point of diminishing practicality is soon reached with the traditional methods of reducing the pressure responsive area of valves of this type. A narrower contact surface seal reduces the pressure responsive area, but at the risk of reduced structural integrity and reduced seal path dimension. A smaller diameter seal reduces the pressure responsive area but encounters difficulties because of the very small manufacturing and alignment tolerances that are presented and the reduced flow path dimension.
Another category of shear seal valve involves rotary seal elements. Rotary shear seal type valves have long been used, such as disclosed in U.S. Pat. No. 3,556,151 to Masuda and U.S. Pat. No. 3,014,499 to Barksdale. These also require torsional actuation force to slide at least two seals in an arc on the seal plate.
An improved valve mechanism having the reliability of shear seals without their typically high power consumption would be desirable.